Manufacture of petroleum naphthalene



July 6, 1965 o. c. EUBANK 3,193,592

MANUFAGTURE OF PETROLEUM NAPHTHALENE 0564/? C. 50E/JAN( BY 52,4% Q MJS Arme/VFY July 6, 1965 o, c, EUBANK 3,193,592

MANUFACTURE OF PETROLEUM NAPHTHALENE Filed Aug. ll. 1961 2 Sheets-Sheet 2 United States Patent O 3,193,592 MANUFACTURE UF PETRULEUM NAPHTHALENE Oscar C. Enbank, Long Beach, Calif., assigner to Union Oil Company of California, Los Angeics, Calif., a corporation of California Filed Aug. 1i, 196i, Ser. No. l3,26 13 Claims. (Cl. 26h-672) This invention relates to the manufacture of naphthalene from source materials of petroleum origin, and in particular concerns an improved process for the production of naphthalene by the catalytic or thermal dealkylation of alkyl-substituted naphthalenes obtained from various petroleum refining operations.

The expanding use of naphthalene for the production of dicarboxylic acids useful in manufacturing synthetic resins and fibers has created considerable interest in the manufacture of naphthalene from petroleum hydrocarbons. It is well known that certain hydrocarbon fractions obtained in various petroleum refining operations, e.g., cracking and reforming, contain considerable quantities of alkylnaphthalenes which can be thermally or catalytically dealkylated to form free naphthalene. As such processes are conventionally carried out, a feedstock consisting of a reformate or cycle oil fraction boiling above about 430 F. and comprising alkylnaphthalenes and such nonnaphthalenic materials as alkylbenzenes, alkyltetr-alins, alkylindanes, etc., is subjected to dealkylating conditions to obtain an effluent product which, after separation of normali gaseous materials such as hydrogen and low molecular weight hydrocarbons, is fractionally distilled to obtain (l) a light gasoline fraction, (2) a naphthalene fraction, and (3) a heavy fraction comprising unreacted alkylnaphthalenes which, aft-er the removal of heavy ends and polymers, is recycled to the reaction zone. According to one mode of operation, the naphthalene fraction is taken over a relatively wide boiling range, eg., from about 400 F. to about 435 F., and the naphthalene is recovered therefrom in pure form by low temperature crystallization. However, the relatively low naphthalene content of such a wide boiling range fraction necessitates the processing of a relatively large volume of material and consequently requires the provision of very extensive chilling and crystallization facilities and the cost of refrigerating a large volume of material other than the desired naphthalene. According to a second mode of operation, the naphthalene fraction is taken over a very narrow boiling range, eg., 420-427 F., and as such is 0f sufcient purity to meet many requirements, eg., conversion into phthalic anhydride. However, when following such mode of operation an appreciable amount of the naphthalene is lost to the gasoline fraction. This occurs by reason of the fact that part of the naphthalene present in the reactor effluent distills over at temperatures below v' about 420 F. in the form of low boiling azeotropes with other components of the eiiiuent. A portion of the naphthalene is also lost to the heavy fraction boiling above about 430 F., but since such fraction is recycled to the reaction zone the naphthalene contained therein is eventually recovered in `substantially pure form.

The present invention is directed to an improved method for carrying out the second of the above-described procedures, and has for its principle object the recovery of the naphthalene which is ordinarily lost to the gasoline fraction in the form of low-boiling azeotropes. A more general object is to provide animproved method for producing naphthalene by the dealkylation of alkylnaphtha- Iene-containing hydrocarbon mixtures of petroleum origin, and in particular to provide a means for recovering by distillation alone and in a high state of purity substanice tially all of the naphthalene present in the dealkylation reactor `effluent. Other objects of the invention will be apparent to those skilled in the art as the description thereof proceeds.

I have now found that the foregoing objects and attendant advantages may be realized in a process in which the dealk lation reactor effluent is first treated to remove normally gaseous constituents, and the remaining liquid portion is fractionated to obtain (l) a light gasoline fraction which is essentially free of naphthalene, (2) an intermediate fraction containing azeotropes of naphthalene and non-naphthalenic components lof the effluent, (3) a naphthalene fraction containing at least about weight percent of naphthalene, and (4) a heavy fraction comprising a small amount lof naphthalene, unconverted alkylnaphthalenes, and materials boiling above naphthalene; and the said intermediate fraction and at least a part of said heavy fraction is thereafter returned to the deakylation zone. More particularly, I have found that those components of the feedstock which form low-boiling azeotropes with naphthalene are only slowly converted to non-azeotrope-formers when subjected to dealkylating conditions sufficient to effect dealkylation of alkylnaphthalenes, but that they c-an eventually be substantially 4completely converted to non-azeotrope-formers by repeated exposure to such conditions; on the other hand, the naphthalene contained in such azeotropes is but slightly aected by reexposure to such conditions. Accordingly, by returning the azeotrope-containing fraction to the reaction zone, the non-naphthalenic azeotropeformers are recycled to extinction and substantially all of the naphthalene which is normally contained in such fraction is recovered in substantially pure form in thev higher boiling naphthalene fraction. As will be apparent, operation in the manner of the invention permits elimination of elaborate chilling and crystallization facilities and the cost of refrigerating a large volume of material, but attains substantially complete recovery of all the available naphthalene at the cost lof conducting a relatively small additional distillation operation.

ln the drawings which form a part of this application, FIGURE l thereof takes the form of a flow sheet illustrating one way in which the principle of the invention has been applied to a typical catalytic hydrodealkylation process, and FIGURE 2 illustrates in flow sheet form an alternative mode of operation as applied to a thermal dealkylation process. In the interests of simplification, such conventional process equipment as pumps, heat exchangers, reboilers, condenscrs, reflux lines, phase separators, valves, instrumentation, etc., have been omitted from the drawings.

Referring now to FIGURE l, the major items of processing equipment include reactor feed column i2, catalytic reactor 14, high pressure gas separator 16, low pressure gas separator 18, light gasoline column 20, naphthalene column 22, and recycle column 24. The latter receives a relatively wide boiling range fraction containing naphthalene as such and in the form of low-boiling azeotropes with non-naphthalenic materials, and serves to separate said azcotropes as an overhead fraction which is returned to the reactor for destruction of the non-naphthalenic azeotrope-formers as previously described. The fresh feed, which is suitably an essentially naphthalene-free heavy reformate fraction boiling between about 435 F. and about 735 F., and containing alkylnaphthalenes and non-naphthalenic materials of the same boiling range, is introduced into the system via feed line 26 and is therein joined by a heavy recycle stream flowing in heavy recycle line 23 and containing unconverted alkylnaphthalenes from a previous cycle of operation. The mixture of fresh feed and heavy recycled material passes from line 26 into feed column i2 which suitably takes the form of a 20- The overheadvfractionfrorn feed column 12 is passed via line 32 into reactor feed manifold 34 wherein it is 'joined by light recycled hydrocarbon material flowing in light recycle line 36, and by a mixture of water vapor and a hydr,'ogen-containing recycle gas stream flowing in line 38K.r l Maikel-up hydrogen and water are introduced Vinto line 38 from lines 4t) and 42, respectively. The reactor feed mixture, comprising the hydrocarbons taken over-y head from column'12, azeotropic naphthalene owingin line 36, hydrogen and water, is passed to reactor feed heater 44 wherein it is heated to an incipient reaction temperature, andjthe heated reactor feed is passed via line 4,6 to catalytic reactor 14 at such rate that the space velocity within the reactor is about 0.4 volume of hydrocarbonper hour per volume of catalyst. About 8100 s.c.f. of hydrogen and about 0.085 barrel of Water are provided per barrel of hydrocarbon in the reactor feed mixture. i Reactor 14 contains a fixed bed of a dealkylation catalyst consisting of a silica-stabilized aluminabase having supported thereon about 3.0 weight percent of cobalt oxide, about 9.0 weight percent of molybdenum oxide, and about 2.2 weight percent of sodium oxide. The reaction zone is maintained at a temperature of about 1100 F. and a pressure of about 1000 p.s.i.g., and a substantinally uniform temperature profile within the catalyst bed is maintained by introducing a quench gas consisting of a part of the hydrogen-containing recycle gas flowing in line 38 into the reaction zone at a plurality ,of'points along the length thereof via lines 47. About 1430 s.c.f. of the quench gas are employed per barrel of hydrocarbon in the reactor feed.

'The reactoreffluent passes from reactor 14'tl1'rough eluent cooler 48 wherein it is cooled to about 160 F., and thence into high pressure separator -16 which is operated at a pressure onlyslightly below that of reactorr14. Within separator'l, the cooled eluent separates into a gaseous phase, a liquid hydrocarbon phase, andan aqueous phase.V The latter is Withdrawn'via line 50 and is either discarded or recycled back to the reactor feedy manifold. The gaseous phase, which comprises hydrogen anda relatively' small amount ofrnormallyv gaseous hydrocarbons, is withdrawn from separator 16 and passed to line 38 for use as the reactor quench gas and for'recycle to the reactor feed manifold. The liquid hydrocarbon phase in separator 16V Column 20 is operated to produce a substantiallyV naphthalene-free light gasoline fraction in overhead linek 60. As is hereinafter more fully discussed, the cutpoint will vary somewhat depending upon a number of factors, but will typically be about 400 F .Y The bottoms fraction from column 20 is,l passedvia transfer line 62 to naphthalene `column 22 which is operated to produce an Voverhead fraction boiling between about 400 andabout 430 F.

and consisting of naphthalene and non-naphthalenic materials which form low boiling azeotropes with naphtha lene. The'bottoms fraction from vcolumn 22, consisting of column 24. As previously stated, the latter serves to separate non-naphthalenic components plus whatever naphthalene is associated therewith in the form of low-boiling azeotropes. Typically, column 24 is operated at a cut point of about 420 F. so that the bottoms fraction has a boiling range of labout 420-425 F. and contains about 98.5V weight percent of naphthalene, and the overhead fraction has a boiling range of about 400-420V F. The latter is returned to the reactor feed manifold 34 via light hydrocarbon recycle liner 36, whereas the bottoms fraction is passed to storage via line 66 as the naphthalene product 4of the process.

Considering now the process of the invention in somewhat greater detail, it is adapted to the dealkylation of any petroleum hydrocarbon mixture containing alkylnaphthalenesV and materials which, in the dealkylated product cause the formation of low-boiling azeotropes with naphthalene. Catalytically or thermally cracked cycle oils and heavy reformate fractionsrare most commonly employed, with platinum catalyzed reformate fractions being particularly preferred. A particularly preferred process feedstock of this type consists of a platinum-catalyzed reformate fraction boiling between about 435 F. and about 675 F. and comprising 40-70percent alkylnaphthalenes. A second preferredV feedstock consists of a thermally or Catalytically cracked cycle oil extract fraction obtained, for example, by subjecting a TCC or yFCC cycle Voil of suitable boilingV range to hydrorening (i.e., hydr-odesulfurization and/or hydrodenitrogenation)v in the presence of a cobalt molybate catalyst (Unining), and subjecting the hydrorefmed product to solvent `extraction (e.g., with sulfur dioxide or a glycol) to obtain an extract product rich in naphthalene and naphthalene precursors. Alternatively, the cycle oil can first be solvent extracted and the aromatics-rich extract then hydrorened to obtain a suitable feedstock. With particularly clean cycle oils (i.e., low sulfur and/0r low nitrogen) the hydrorening step can be omitted. Also, when the dealkylation reaction'is effected thermally, the pre-removal of sulfur `and/ or nitrogen from the feedstock need not be complete, and some instances (depending on the sulfur and nitrogen specifications for the naphthalene product) may be omitted entirely.

Since theproeess of the invention is directed to the recoveryin substantially pure form of the naphthalene which heretofore has been lost inr the form of low-'boiling azeotropesr, and since the non-naphthalenic hydrocarbons which form such Iareotropes'with naphthalene occur in the reactor effluent regardless .of whether the dealkylation reaction iseffected Catalytically or thermally, the advantages of the process are attained with both types of operation. When carried out catalytically, the reaction is usually effected in the presence of hydrogen, and the catalyst usually comprises an oxide or sulfide of one or moreof the Ymetals of groups VIB and VIII of the periodic i Vactivity are preferablyk deactivated by including minor amounts of alkalizing components, e.g., sodium oxide, in the catalyst composition. The catalyst may be maintained in the' form of a fixed bed, a compact moving bed, or a fluidizedl bed. Typical catalytic dealkylation conditions include a lreaction temperature between about 900 IFQand fabout 1150 F., a reaction pressure between about 700 and aboutl'600 p'.s.i.g., and a liquid hourly space velocity of between about 0.2 Iand about 5y volumes of'hydr-ocarbon per hour per volume of catalyst. When the reaction is carried out in the presence of hydrogen, as is usually the case, between about 3000 and about 15,000 s.c.f. of

hydrogen (usually in the form of a recycle gas containing 70-95 volume percent of hydrogen) are provided per barrel of hydrocarbon. The use of water vapor to moderate the reaction in accordance with the teachings of Doumani, U.S. Patent No. 2,734,929, is a valuable expedient, with the water vapor being provided in an amount representing between about 0.04 and Iabout 0.15 barrel of liquid water per barrel of hydrocarbon. When employing a xed bed catalyst it is also desirable to maintain the temperature gradient within the bed at a. value below about 100 F. by introducing a hydrogen-containing quench gas into the reaction zone at a plurality of points along the length thereof as described previously in connection with FIGURE l.

Typical thermal dealkylation conditions include a reaction temperature between about l000 F. and about 1500D F., preferably between about ll F. and about l250 F., a reaction pressure between about 200 and about 1000 p.s.i.g., and a reaction time of between about 2 and about 2O seconds. Conventionally, thermal dealkylation is likewise carried out in the presence of hydrogen, with between about 2000 and about 10,000 s.c.f. of hydrogen being provided per barrel of hydrocarbon. lt is also conventional to ei'ect thermal dealkylation within a fixed, compact moving, lor fluidized bed of a noncatalytic inert material, such as sand, pebbles, alundum chips, and the like.

ln general, then, the dealkylation reaction may be carried out under any of the wide variety of conditions known to effect the dealkylation of alkyl-substituted hydrocarbons such as alkylnaphthalenes.

The eiiluent which is withdrawn from the reaction zone is initially treated to separate gaseous from liquid constituents, eg., by condensation. When hydrogen is employed `in the reaction zone it is preferably recovered as a separate gaseous stream for recycle purposes by initially condensing the reactor effluent at an elevated pressure, after which the normally gaseous hydrocarbons (which for the most part have remained dissolved in the liquid hydrocarbon components) are iiashed off by reducing the pressure to a substantially lower value, eg., atmospheric pressure. The remaining liquid components of the reactor eflluent are then passed to the fractionation operation which constitutes the heart of the invention.

As previously stated the fractionation operation is cari naphthalene fraction which contains at least about 95 n weight percent of naphthalene, and which is taken as the major process product; (4) a heavy fraction which contains unconverted alkylnaphthalenes and non-naphthalenic hydrocarbons of similar boiling range, and which is recycled to the reaction Zone; and (5) a high-boiling fraction which comprises polymeric materials and the like and which is taken as a process by-product useful as fuel oil and the like.

lt will be apparent that while certain of the cut points between these respective fractions are more Critical than others, a certain degree of latitude is permitted depending on the desired purity of the naphthalene fraction and the extent to which it is desired to recover the napht'nalene which occurs in the form of low-boling azeotropes. Also, the cut points will vary somewhat with the various process parameters. Thus, in FIGURE l, the cut point at which the light gasoline column 2t) is operated to produce the first of the above-identified fractions will depend upon the boiling points of the naphthalene-containing azec-tropes present, which boiling points in turn depend upon the nature of the feedstock and the reaction conditions. However, once steady state operating conditions are attained the exact cut point can be determined by gradually raising the column head temperature until naphthalene first appears in the distillate. While maximum recovery of naphthalene will be achieved when the cut point is so selected that the overhead fraction is entirely free or naphthalene, the cost of operating at high reflux ratios and of subsequently handling an increased volume of material frequently outweighs the value of the additional naphthalene recovered. Accordingly, under some conditions it is permissible, and even desirable, that the first fraction contain a small quantity, less than about l weight percent, of naphthalene. As a general rule, optimum operation is attained when the fractionation is carried out to produce a rst fraction having a maximum true boiling point between about 395 F. and about 405 F., usually about 400 F.

The cut point between the second and third of the aboveidentiiied fractions is somewhat less critical than that between the first and second fractions, and is primarily dependent on the desired purity of the naphthalene product. Where maximum recovery, rather than maximum purity, of the naphthalene product is the primary Consideration, such cut point may be set relatively low, eg., at about 415 F. Gn the other hand, a more highly purified naphthalene product may be obtained {at the expense of losing some of the non-azeotroped naphthalene to the rst fraction) by setting the cut point somewhat higher, eg., at about 420 F. or even slightly higher. Thus, in FIGURE l, column 24 is usually operated to produce an overhead fraction having a maximum tru-e boiling point between about 415 F. and about 420 F.

The cut point between the third and fourth of the aboveidentiiied fractions is governed by the same consideration discussed above with respect to the second and third fractions. By setting the cut point at a relatively low value, eg., at about 425 F., a high concentration of naphthalene is obtained in the third fraction at the expense of losing some naphthalene to the fourth fraction (which naphthaiene, however, is eventually recovered), whereas by setting such cut point at a relatively high value, eg., at about 435 F., a somewhat less concentrated naphthalene procluct is obtained. Phus, in FIGURE. l, column 22 is operated to produce an overhead fraction having a maximum true boiling point between about 425 F. and about 435 F., preferably between about 425 F. and about 430 F.

The cut point between the fourth and fth of the aboveidentified fractions is least critical of all, and is governed primarily by the nature of the deallsylation step and the feedstock employed. Desirably, such cut point is selected to separate materials capable of further dealkylation from materials which undergo no useful reaction in the deallrylation zone. Usually, the latter materials boil above about 485 F., so that, in FIGURE l, column l2 is operated to produce an overhead fraction having a maximum true boiling point of at least about 485 F., but not greater than about 550 F., preferably of about 510 F.

The following table summarizes the operation of the fractionation section of the processing system of the invention:

Boiling Range, F. Frtetion Principal Component Operable Preferred 1 Light Gasoline XB P-405 IB P4100 Azeotroped N aphthalene. 395-420 40G-420 Naphthalene 415-435 420-430 Allrylnaphthalenes 425-550 430-510 Polymers, etc. 550 510 Referring now to FIGURE 2, the process thereby illustrated employs thermal dealkylation and an alternative mode for producing the above-described eluent fractions. The feedstock, which consists of a platinum-catalyzed reformate fraction boiling over the range 435-570 F.

and containing about 43.7 weight percent of mono-methylnaphthalenes, about 33.0 weight percent of higher alkylnaphthalenes, with the remainder being non-naphthalenic hydrocarbons, is introduced into the process system via line 100 and is therein joined by the liquid portion of the reactor efuent flowing in line 102. The mixture is introduced into feed column 104 which is ,operated to produce in line 106 an overhead fraction having a maximum boiling point of about 510 F. Said fraction is introduced from line 106 into reactor feed manifold 108 along with a recycle stream iiowing in recycle line 110. The-bottoms fraction from feed column 104 is passed to storage via line 112.

The reactor feed mixture flowing in manifold 108 is admixed with about 5000 s.c.f./'bbl. of hydrogen introduced into the system from line 114, and passes through feed preheater 116 which is operated to preheat the reactor feed to about 900 F. The heated feed then passes to reactor 118 within which the dealliylationl is effected. Reactor 118 consists of a tire-brick lined shell filled with one-inch alundum balls, and is maintained at a temperature of about 1325 F. and a pressure of about 650 p.s.i.g.

VThe reactor feed is passed therethrough at such a rate as to maintain a contact time therein of about l seconds.

The hot reactor effluent is withdrawn from the reactor through line 120 to etiluent cooler 122 wherein it is cooled to ambient temperature, and the cooled and condensed eluent is passed to gas-liquid separator 124 to effect separation of normally gaseous components. The latter are withdrawn through line 125 as a product make gas which may be employed as such for fuel or treated by conventional methods to separate a hydrogen-rich stream suitable for recycling to reactor feed manifold S. The liquid portion of the reactor effluent is withdrawn from separator 124 and is passed via line 12S to gasoline column 130.

Column 130 is operated to produce in line 132 an overhead fraction having a maximum boiling point of about 420 F. Said fraction is introduced from line 132 into light gasoline column 134 which is operated to produce in line 136 an overhead fraction of substantially naphthalene-free light gasoline boiling below about 400 F. The bottoms fraction from column 134, boiling ybetween about 400 F. and about 420 F. and containing azeotroped naphthalene, is introduced into recycle line 110 for return to reactor feed manifold 110.

The bottoms fraction from column 130 is passed via transfer line 138 to naphthalene column 140 which is operated to produce in overhead line 142 a naphthalene product distilling between about 420 and about 427 F.

and containing about 97.6 weight percent naphthalene.

The bottoms fraction from column 140, consisting .of

claims, or the equivalent of such stated step or steps, be

employed.

I, therefore, particularly point out and distinctly claim as my invention:

1. In a process wherein an alkylnaphthalene-contain- Y ing feedstock is passed through a dealliylation zone maintained under fdealkylating conditions of temperature and pressure to obtain a dealkylation zone effluent comprising naphthalene formed in said zone by dealkylation of said allyl-naphthalenes and non-naphthalenic hydrocarbons which form low-boiling a'zeotropes with said naphthalene, the improvementV which comprises fractionating said effluent to obtain a rst fraction containing at least about 95 weight percent of naphthalene, a second fraction having a. boiling range below that'of said first fraction and cornprising azeotroped naphthalene, and a third fraction hav-Y ing a boiling range above that of said first fraction and comprising alkylnaphthalenes; and returning said second fraction and an alkylnaphthalene-containing portion of said third fraction Yto said dealkylation zone.

2. A process as defined by claim 1 wherein said second fraction is further fractionated to obtainv a low-boiling substantially naphthalene-free portion and a higher-boiling portion comprising azeotroped naphthalene; and said higher-boiling portion is ,returned to said dealkylation zone.

3. A process as defined by claim 1 wherein said dealkylation zone contains a dealkylation catalyst comprising an active component selected from the class consisting of the oxides and sulfides of the metals of groups VEB and VIII of the periodic system, and the said feedstock is contacted with said catalyst in the presence of added hydrogen.

4. A process as dened by claim 1 wherein said dealkylating conditions are sufficient to effect a substantial degree of dealkylation in the absence of a catalyst.

5. A process as defined by claim 1 wherein said dealkylation Zone contains a catalyst comprising a mixture of the oxides of molybdenum and cobalt supported on an falumina base, and is maintained at a temperature between about 900 F. and about l250 F. and a pressure between about 700 p.s.i.g. and about 1600 p.s.i.g., and hydrogen is introduced into said dealkylation zone in an amount representing between about 3000 s.c.f. and about 15,000 s.c.f. per barrel of hydrocarbon introduced into said zone.

6. A process as deiined by claim 1 wherein said dea'lkylation zone contains a non-catalytic solid material,

Y and is maintained at a temperature between about 1000 F. and about l500 F. and at a pressure between about 200 p.s.i.g. andabout 1100 p.s.i.g., and hydrogen is introduced into said dealkylation zone in an amount repreialkylnaphthalenes; ('3) withdrawing a dealkyla-ted efduent containing a substantial amount of naph-thalene lfrom said dealkylation zone and condensing said effluent to obtain ia liquid eflluent phase and a gaseous effluent phase; (4) distilling said liquid effluent phase to obtain: (a) .a substantially naphthalene-free tirs-t fraction having a maximum boiling point below about 405 F., (b) a higherboiling second fraction having a maximum boiling point between about 395 F. and ,about 420 F., and containing azeotroped naphthalene, (c) a higher-boiling third fraction having a maxi-mum boiling point between about 415 F. and about 435 F., and containing at least about weight percent of naphthalene, and (d) a higherboiling fourth fraction having a maximum boiling point below about 550 AF. and comprising unconverted alkylnaphthalenes; l(5) returning .said second fraction to the aforesaid Istep (1) Ias said light recycle stream; and (6) returning said lfour-th fraction to the 4aforesaid step (l) as said heavy Vrecycle stream.

8. A process as deiined by cla-im 7 wherein said dealkylation zon-e contains a dea-lkyla-tion catalyst comprising Van active component selected from the class consisting of the oxides and suldes of the metals of groups VIB and VIII of lthe periodic system, and the said feedstock is contacted with'said catalyst'in :the presence of added hydrogen. l

9. A processes dened by claim 7 wherein said dealkylat-ing condit-ions are suicient to effect a substantial degree of dealkylation in Ithe absence of a catalyst.

10. A proces-s as defined by claim 7 wherein sa-id de- ;alkylati-on zone contains a catalyst comprising -a mixture of the oxides yof molybdenum Iand cobalt supported on an alumina base, and is main-tained at a temperature between about 900 F. and :about 1250 F., and at a pres- Sure between about 700 p.s.i.g. .and about 1600 p.rs.i.g., and hydrogen is introduced into ysaid dealkylation zone in an amount representing between about 3000 s.c.f. and .about 15,000 s.c.f. per barrel of hydrocarbon introduced into :said zone.

11. A process as defined by claim 7 wherein said dealkyla-tion zone contains .a non-catalytic solid material, and is maintained Iat la tempera-ture between about 1000 F. and about 1500 F. :and at a pressure between about 200 p.s.i.g. and about 1100 p.s.i.g., and hydrogen is introduced into said dealkylation zone in an amount representing between about 2000 s.c.f. and labout 10,000 scf. per barrel of hydrocarbon introduced into said zone.

I'12. The process -for obtaining naphthalene which comprises (1) forming a feed mix-ture comprising the hereinafter identified heavy recycle stream, the hereinafter identified light recycle stream, a platinum-catalyzed petroleum hydrocarbon ref-ormate fraction boiling above about 430 F. and containing a substantial amount of alkylnaphthalenes, and between about 3000 and about :15,000 s.c.f. of hydrogen per barrel of hydrocarbon; (2) contacting said feed mixture with a fixed bed of a dealkylation catalyst comprising a mixture of the oxides of molybdenum and cobalt supported on silica-stabilized alumina containing a minor amount of an alkali, said contacting being elected at a liquid hourly space velocity of between about 0.2 and about 5 volumes of hydrocarbon per hour per volume of catalyst and .at .a temperature between about 900 F. and about 1250 F, and a pressure between about 700 and about 1600 p.s.i.g.; (3) Withdrawing ra dealkyla-ted eiuent containing a substantial amount of naphthalene from said dealkylation zone and lfractionating it -to obtain: (a) .a normally gaseous fraction, (b) a substantially naphthalene-free light gasoline fraction having a boiling point of about 400 F., (c) a higher boiling naphthalene-containing iirst intermediate fraction having a maximum boiling point of about 420 -F., (d) a naphthalene fraction containing lat least about weight percent naphthalene, and (e) a higher boiling alkylnaphthalene fraction having a maximum boiling point of Iabout 550 F.; (4) returning said second intermediate fraction to the aforesaid step (1) as said light recycle stream; and (5) returning said alkylnaphthalene fraction to the aforesaid step 1) as said heavy recycle stream.

.13. A process as deiined -by claim 12 wherein said catalyst comprises a silica-stabilized alumina base having distended thereon about 3 weigh-t percent of cobalt oxide, about 9 weight percent of molybdenum oxide, and about y2.2 Weight percent of sodium oxide, and said feed mixture contains water vapor in an .amount corresponding to between about 0.04 and about 0.15 bar-rel of liquid water per barrel of hydrocarbon, and hydrogen is introduced into said catalyst bed .at a plurality of points along the length thereof and in an amount sufficient to maintain the temperature therein at a value below about F.

References Cited bythe Examiner UNITED STATES PATENTS 2,694,095 ll/ 54 Medoalf et al 260-672 2,858,348 10/58 Bosmajiau et al 260-674 ALPHONSO D. SULLIVAN, Primary Examiner.

JOSEPH R. LIBERMAN, Examiner. 

1. IN A PROCESS WHEREIN AN ALKYLNAPHTHALENE-CONTAINING FEEDSTOCK IS PASSED THROUGH A DEALKYLATION ZONE MAINTAINED UNDER DEALKYLATING CONDITIONS OF TEMPERATURE AND PRESSURE TO OBTAIN A DEALKYLATION ZONE FFLUENT COMPRISING NAPHTHALENE FORMED IN SAID ZONE BY DEALKYLATION OF SAID ALKYL-NAPHTHALENES AND NON-NAPHTHALENIC HYDROCARBONS WHICH FORM LOW-BOILING AZETROPES WITH SAID NAPHTHALENE, THE IMPROVEMENT WHICH COMPRISES FRACTIONATING SAID EFFLUENT TO OBTAIN A FIRST FRACTION CONTAINING AT LEAST ABOUT 95 WEIGHT PERCENT OF NAPHTHALENE, A SECOND FRACTION HAVING A BOILING RANGE BELOW THAT OF SAID FIRST FRACTION AND COMPRISING AZETROPED NAPHTHALENE, AND A THIRD FRACTION HAVING A BOILING RANGE ABOVE THAT OF SAID FIRST FRACTION AND COMPRISING ALKYLNAPHTHALENES; AND RETURNING SAID SECOND FRACTION AND AN ALKYLNAPHTHALENE-CONTAINING PORTION OF SAID THIRD FRACTION TO SAID DEALKYLATION ZONE. 